AVB defines low latency Class A traffic with a maximum latency of 2 ms over 7 hops and higher latency Class B traffic with a maximum latency of 50 ms over 7 hops. Audio streaming standards, such as AVB 61883-6 Audio Format, suggests “A Class A isochronous packet is generated every 8 kHz.” In such audio formats, such a packet represents 125 μs worth of audio. Accordingly, an audio CD type (16 bit sample, stereo) stream at 48 kHz generates 6 samples, which implies 24 Bytes of payload. In examples where 2 ms worth of audio is buffered, sending audio data at 125/250 μs interval may pose a challenge with respect to implementation.
Class AB traffic is configured to be shaped or scheduled with a 125/250 μs interval rate. Queuing of a particular class of AVB stream is typically configured such that only MaxIntervalFrames of each stream may be scheduled within one scheduling cycle (125 μs for class A, 250 μs for class B). Accordingly, a software scheduling task is to be run at the frequency of the scheduling cycle (125/250 μs). On a preemptive Multitasking Operating System (e.g. Linux, QNX, Windows) a scheduling cycle of 125/250 μs is not very feasible, and if implemented as interrupt service routine, the additional load of this overhead may drastically lower system performance.